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How our immune systems influences the microbiome on our skin
Introduction A microbiome is a community of microorganisms that can both be symbiotic and pathogenic. We now know that there is a difference between apparent colonization and infection. As we learn more about complex microbial communities we will be better able to understand the complex interactions between microbes with the microbiome as well as host-microbial interactions. Currently, about unique phyla are found in various microbiomes compared to the hundreds that exist in environmental communities. The advance in sequencing technology has allowed us to begin to study these complex communities. Using high-throughput sequencing techniques we are able to identify unculturable microbes that would previously go undetected 2. The immune systems role It been shown that microbes educate the immune system with elevated T-cell expression in hair folicles and other areas with increased colonization. Interestingly, this colonization and response of microbes on the skin effects our gut flora 2. The role of our immune system on the colonization is less understood. Oh et al. asked how our immune system shapes the microbe community on our skin 1? Microbes on skin Our skin is our primary defense against harmful microbes, but there is a symbiotic relationship between our skin and the microbial environment. Skin diseases, such as psoriasis, have shown to disrupt the equilibrium and colonization of the skin. Healthy skin has a different community of microorganisms than dry, moist, or sebaceous skin and diseased skin can be even worse 2! Experimental Design To begin addressing the effect of our immune system on the microbiome of our skin Oh et al. looked at colonization of primary immunodeficiency (PID) patients. Using PID patients as a model they could analyze how different immunity states effect the microbiota, and how these microbes interact with our skin to cause disease. PID patients suffer from recurring skin infections by both common and rare opportunistic pathogens probably due to their decreased levels of T and B cells. To determine PID patient cohorts and/or a clinical history with genetic testing was used to increase the chances of seeing a result. If less severely immunocompromised patients were accidentally included then results make have been masked. The table to the right shows the breadth of participants. Twenty-four hours prior to the skin scraping patients were directed to avoid bathing, anitmicrobial soap, shampoos and ointments. This was to try to eliminate confounding factors. The samples were taken from the forearm, elbow crease, behind the ear and nose. Immediately after obtaining the samples they were prepared and sent for sequencing. There was a healthy control group and patients undergoing antimicrobial treatment as well. The forearm was used as a control as well, this sight is less likely to exhibit increased colonization due to location. Findings The sequencing results yielded a large change in the microbiota of immunocompromised individuals than that of the controls. There is a drastic change in the colonization of the elbow crease (Af), depicted by the large yellow bars. Even though there is less of a change in the colonization of the skin behind the ear (Ra) it is still starkly different. All of the sampling areas had an increase in firmicutes highlighted in the piecharts. Staphylococcus infections are commonly treated in PID patients. To further characterize the results they performed various statistical analyses. Some of these analyses looked at the quality of the data, principal correlation analysis, and others examined bacterial-fungal interactions. They found an increased permissibility in both bacterial and fungal species in PID patients. The diversity of the microbe community was also altered with an association with opportunistic pathogens with severity. Lastly, they were able to identify some co-colonizing bacterial and fungal microbes. They suggested the PID allows the skin to be colonized by atypical microbes but there is not an increase in novelty or diversity or the biota. There may be a lack of new phyla because different areas of the body are better inhabited by different microbes. In conclusion, Oh et al. have begun to demonstrate the immune systems role on our skins microbiome. There is still a lot of work to be done but it will be very beneficial to understand our immune system's effect on the microbial community. This will be of particular interest to immunocompromised people such as, PID, cancer, transplant and HIV patients 1. References 1 Oh J. et al. 2013. Genome Res. 23:2103-2114 PMID:24170601 2 Naik S. et al. 2012. Science. 337:1115-9. PMID:22837383